Dynamic braking; streetcars of Kenosha, Wis.

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Dynamic braking was a breakthrough created more than 50 years ago as a way to make diesel freight operations safer and more efficient, especially in territory involving difficult grades. It’s a method of train braking in which the kinetic energy of a moving train generates electric current at the locomotive traction motors. It works like this: While the train is coasting, the engineer uses a controller (on some units, the throttle also handles this function) to energize the tractionmotor fields, causing the motors to act as generators. The resistance of the motor field acts as a brake. The resulting electric current creates heat dissipated in banks of resistors located in the carbody. Dynamic braking supplements a train’s air brakes, although on most freight railroads, the dynamics are essential to train handling. Although originally intended for mountain territory, dynamic braking has become standard for nearly all new diesels, passenger or freight. The only external evidence of dynamics is the grilles covering the resistor grids, located directly behind the operator cab on contemporary GEand GM-design diesels. Until the advent of EMD’s SD50 of 1981, the dynamic brake resistors on GM engines were located in the middle of the long hood, above the prime mover, visible as pronounced bulges or “blisters.” — Kevin P. Keefe

Q

Watching recent TV news coverage in Kenosha, Wis., I saw what looked like a 1920sera streetcar go past. What’s the story? — Joseph E. Herbert

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You caught a glimpse of Kenosha’s Lakefront Trolley, a small streetcar system opened in 2000 as a way of connecting the city’s Metra commuter station with the Lake Michigan waterfront. The operation consists of PCC-style cars. The PCC is a streamlined design created in the late 1930s by a traction consortium called the Presidents’ Car Committee. Most were built by St. Louis Car Co., but the six original Kenosha cars are 1951 products of Canadian Car & Foundry, constructed under license for Toronto’s sprawling street railway system. — Kevin P. Keefe

Greg McDonnell A Union Pacific SD38-2 equipped with dynamic braking exhibits the distinctive “blister” midway along the hood behind the cab that was used on earlier EMD locomotives. With its huge roster, UP avoids duplicating locomotive numbers by using the “UPY” reporting marks on many units that are assigned to yard and local service.

Robert S. McGonigal A PCC-style car in the livery of the Johnstown (Pa.) streetcar system plies the streets of Kenosha, Wis.